Apart from the obvious safety aspects, incorrect prop choice probably causes more problems in electric flight than any other mismatched component, and it is SO easy to get right, as long as you have the correct equipment.
The equipment Iím referring to is some sort of measuring device such as a Wattsmeter or Power Meter, and these are available from most model shops now at very low cost.
There was a time when even I used to poke about in the dark, trying to establish whether or not I had chosen the correct prop by how hot the motor or NiCad pack got after a couple of minutes! Looking back it was crazy!
When you consider the cost of a melted motor, blown ESC or overloaded Li-Po, paying around £25 for a meter suddenly fades into insignificance and your enjoyment and success in electric flight will suddenly take an upturn, as you will finally be able to see at a glance exactly what is going on.
These meters simply plug in between the flight battery (whether it be a NiMh or a Li-Po) and as you open the throttle of your (well secured) model to full, the various readings instantly indicate the important information you need: current in Amps, power consumption in watts, battery state under load in volts, and in most cases the number of milliamp-hours of battery capacity given up (although this will only be of any use if you are measuring a complete ground run from fully charged to fully exhausted).
As you analyse this information, you can see whether the wattage exceeds the motorís capability, whether the current exceeds the ESC or batteryís constant handling capacity, and whether (in the case of a Li-Po) the battery voltage is being pulled down too low by the current being drawn. It is therefore also very useful in establishing the quality of some of these unknown brands of Li-Po from the Far East - if at 10C it is showing less than 10 volts, then your Li-Po is a lemon.